1. Field of the Invention
The present invention relates to an anisotropically conductive sheet and a connector which are suitable for use, for example, in electrical connection between circuit devices of electronic parts and the like, or in inspection apparatus for circuit devices such as printed circuit boards and semiconductor integrated circuits.
2. Description of the Background Art
An anisotropically conductive elastomer sheet exhibits conductivity only in its thickness-wise direction or has pressure-sensitive conductive path-forming parts exhibiting conductivity only in its thickness-wise direction when it is pressurized in the thickness-wise direction. Since the anisotropically conductive elastomer sheet has features that short electrical connection can be achieved without using any means such as soldering or mechanical fitting, and that flexible connection is feasible with mechanical shock or strain absorbed therein, it is widely used as a connector for achieving electrical connection between a circuit device, for example, a printed circuit board, and a leadless chip carrier, liquid crystal display panel or the like in fields of, for example, electronic computers, electronic digital clocks, electronic cameras and computer key boards.
On the other hand, in electrical inspection of circuit devices such as printed circuit boards and semiconductor integrated circuits, it is conducted to interpose an anisotropically conductive elastomer sheet between an electrode region to be inspected of a circuit device (hereinafter may also be referred to as xe2x80x9ca circuit board to be inspectedxe2x80x9d), which is an inspection target, and an electrode region for inspection of a circuit board for inspection in order to achieve electrical connection between electrodes to be inspected formed on at least one surface of the circuit device to be inspected and electrodes for inspection formed on the surface of the circuit board for inspection.
As such anisotropically conductive elastomer sheets, there have heretofore been known those of various structures. For example, Japanese Patent Application Laid-Open No. 93393/1976 discloses anisotropically conductive elastomer sheets obtained by uniformly dispersing metal particles in an elastomer, and Japanese Patent Application Laid-Open No. 147772/1978 discloses anisotropically conductive elastomer sheets obtained by unevenly distributing particles of a conductive magnetic material in an elastomer to form many conductive path-forming parts extending in the thickness-wise direction thereof and insulating parts for mutually insulating each of them.
However, since such an anisotropically conductive sheet is in the form of a flat plate both surfaces of which are smooth, or of a flat plate as a whole despite the surfaces of the conductive path-forming parts thereof slightly project from the surfaces of the insulating parts thereof, the following problem is offered when it is used in, for example, electrical inspection of a circuit device to be inspected.
Namely, the circuit device to be inspected may be carried by a carrier in some cases, being held by holding claws of the carrier, which engages with the lower surface of the circuit device at a peripheral edge part thereof, in a state that electrodes to be inspected provided on the lower surface thereof have been exposed. In the anisotropically conductive sheet having an even thickness as a whole, however, a peripheral edge part of the anisotropically conductive sheet comes into contact with the holding claws of the carrier. Therefore, the circuit device to be inspected cannot be accurately arranged or positioned at a prescribed position, and so it is difficult to achieve electrical connection between the electrodes to be inspected of the circuit device to be inspected and the conductive path-forming parts of the anisotropically conductive sheet.
The present invention has been made on the basis of the foregoing circumstances and has as its object the provision of an anisotropically conductive sheet and a connector, which are each capable of achieving its accurate electrical connection easily to a target to be electrically connected even when the target is held and carried by a carrier or the like.
In the aspect of the present invention, there is thus provided an anisotropically conductive sheet comprising an anisotropically conductive functional region part exhibiting conductivity in its thickness-wise direction and an insulating peripheral region part located about the functional region part, wherein the thickness of the functional region part is greater than that of the peripheral region part, and the upper surface of the functional region part is projected from the upper surface of the peripheral region part and connected to the upper surface of the peripheral region part with a difference in level.
The difference in level between the upper surface of the functional region part and the upper surface of the peripheral region part may make a space for inserting a holding tip part of a carrier which engages with the lower surface of a peripheral edge part of a circuit device to be inspected arranged on the upper surface of the functional region part.
In the anisotropically conductive sheet according to the present invention, the functional region part may preferably comprise a plurality of conductive path-forming parts each extending in the thickness-wise direction of the sheet and arranged in a state insulated from one another by insulating parts.
In the anisotropically conductive sheet as above, a ratio A of the thickness of each of the conductive path-forming parts to the maximum diameter thereof may preferably be higher than 1.5, but not higher than 8, and a ratio B of the thickness of the conductive path-forming part to the minimum arrangement pitch of the conductive path-forming parts may preferably be not lower than 1, but not higher than 3.
In the anisotropically conductive sheet as above, a ratio C of the thickness of the functional region part to the thickness of the peripheral region part may preferably be higher than 1, but not higher than 5.
In the anisotropically conductive sheet as above, the size of the difference in level between the upper surface of the functional region part and the upper surface of the peripheral region part may preferably 0.1 mm or greater.
In an aspect of the present invention, there is also provided a connector formed of the anisotropically conductive sheet described above.
According to the construction described above, the functional region part has a greater thickness than that of the peripheral region part, and the upper surface thereof is projected from the upper surface of the peripheral region part and connected to the upper surface of the peripheral region part with a difference in level, whereby a space for inserting a holding tip part of a carrier is defined between a target to be electrically connected and the upper surface of the peripheral region part, and after all it is avoidable for the tip part of the carrier to come into contact with the anisotropically conductive sheet to interfere with the accurate location of the target. As a result, the target can be arranged at the prescribed position, and accurate electrical connection between the target and the anisotropically conductive sheet can be achieved with ease.